CDs@ZIF-8 nanocomposite with built-in ratiometric signal for selective tetracycline detection

Tetracycline (TC), a broad-spectrum antibiotic, poses serious ecological and health risks due to its environmental persistence, making it necessary to develop effective detection methods. Herein, a dual-emission ratiometric fluorescence sensor (CDs@ZIF-8) was developed via a one-potin situencapsulation of blue-emitting N,S-co-doped carbon dots (CDs) within the zeolitic imidazolate framework-8 (ZIF-8). The N,S co-doping strategy significantly elevates the fluorescence quantum yield and enriches surface active sites, ensuring a bright and stable reference emission. The characteristic blue emission of the embedded CDs at 430 nm is efficiently quenched via the inner filter effect (IFE) in the presence of TC, whereas a pronounced emission enhancement at 515 nm was induced by the coordination of TC with Zn²⁺ions from the ZIF-8 framework, which restricts the intramolecular conformational rotation of TC. Consequently, a robust ratiometric response (I₅₁₅/I₄₃₀) was established for TC quantification, yielding a broad linear dynamic range (0-80μM) and a low limit of detection (69 nM), furthermore, exceptional selectivity, long-term stability, and reliable recyclability were systematically demonstrated by the developed sensor. Accurate quantification was further achieved in complex real-world matrices (lake water, honey,and milk), with relative standard deviations ranging from 1.09% to 4.51%. Moreover, a smartphone-based point-of-care testing platform was developed leveraging the distinct color transition from blue to yellow-green, showing great promise for on-site visual quantification. Collectively, this study provides a robust, rare-earth-free ratiometric sensing system with integrated dual-mode detection capability, demonstrating substantial potential for environmental monitoring and food safety assurance.